It has long been the aim of bio-scientists to arrive at an explanation of the mechanism of active ion transport across epithelial membranes. Frog skin is an example of an epithelial membrane which actively transports Na ion ions. In the analysis of the kinetics of Na ion fluxes, the assumption is often made that the epidermis, effectively, consists of one compartment. In recent years we have proposed to consider a more realistic model, based on the histological structure. Applying such a multi-compartment model, we have accuaulated data by the method of computer simulation which are not only consistent with laboratory findings, but which also provide for a broader basis in the analysis of the mechanism of drug and hormone effects on Na ion fluxes within and across frog skin epidermis. In the year ahead we plan to further test in computer studies properties of the multicompartment model and to apply it in studies on the stimulatory effect of catecholamines on Na ion transport with the aim at arriving at clearer understanding of the site of action of these drugs. Bibliographic references: Howell, J.R. and Huf, E.G. Metabolic compartmentation in amphibian skin epidermis. A computer simulation study. Comput. a. Biomed. Res., 8: 72-87, 1975. Huf, E.G. and Howell, J.R. Computer simulation of sodium fluxes in frog skin epidermis. J. Membr. Biol., 15: 47-66, 1974.